An example of a power amplifier system of the prior art is described by referring to FIG. 11. A signal fed in an input terminal 1 passes through a voltage-controlled amplifier 2, and drives a speaker 6, after it is amplified by a power amplifier system 9 comprising a negative feedback circuit 4, a voltage amplifier 3 and a power amplifier 5. In order to prevent the speaker 6 from being input with an excessive power or to avoid a distorted sound due to a wave form being electrically clipped by exceeding a dynamic range, a limiter means has been used in the past, which detects an output of the voltage-controlled amplifier 2, e.g. an input voltage of the power amplifier system 9, converts it into a pulse wave by a voltage comparator 7, converts the voltage into a d.c. signal by integrating it with an integrating circuit 8, and reduces an amplification factor of the voltage-controlled amplifier 2, so as to suppress a wave form distortion of the output.
However, since the composition of the prior art detects and controls only a magnitude of the input signal, it has been unable to control clipping within the power amplifier system 9 itself or clipping at an output stage caused by fluctuation of the power supply voltage, so as to result in a problem of generating a distortion from the speaker.